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Question #42123

Difficulty: 8/10 | 🟢 Free

The Question

A block of mass m=1 kgm = 1 \text{ kg} is attached to a horizontal ideal spring of spring constant k=100 N/mk = 100 \text{ N/m}. The block oscillates in a fluid where the drag force transitions from linear (Stokes regime) to quadratic (Newtonian turbulent regime) depending on the velocity vv, modeled as Fd=−bv−cv∣v∣F_d = -b v - c v |v|, where b=0.4π kg/sb = \frac{0.4}{\pi} \text{ kg/s} and c=0.03 kg/mc = 0.03 \text{ kg/m}. The block is released from rest at a displacement A=1 mA = 1 \text{ m}. Assuming the energy dissipated per cycle is small compared to the total energy (weak damping approximation), what is the approximate total mechanical energy dissipated by the fluid drag during the first quarter cycle (from x=Ax = A to x=0x = 0)?

Options

  • A.

    3 J3 \text{ J}

  • B.

    1 J1 \text{ J}

  • C.

    2 J2 \text{ J}

  • D.

    4 J4 \text{ J}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Reynolds Number Transition|Damped Oscillation Equation (546)|Integration

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to model energy dissipation in a fluid where the Reynolds number transition introduces a nonlinear (quadratic) drag term.

The 'Lethal Collision' occurs when students rely on rote memorization of the standard linearly damped oscillator equation (E(t)=E0e−bt/mE(t) = E_0 e^{-bt/m}) and calculate the energy loss as ΔE≈E0(bt/m)=1 J\Delta E \approx E_0(bt/m) = 1 \text{ J}.

By doing so, they completely ignore the cv∣v∣cv|v| term, which dominates at higher oscillation amplitudes and velocities, leading to a severe underestimation of the dissipated energy.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterMechanical Properties of Fluids - Class 11 Part 2
ConceptReynolds Number Transition
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree